Page 834 - Small Animal Internal Medicine, 6th Edition

806 PART VI Endocrine Disorders

CHAPTER 49
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Disorders of the

Endocrine Pancreas

HYPERGLYCEMIA blood glucose concentration is increasing over time (see
p. 828).
Etiology
Hyperglycemia is present if the blood glucose concentra-
tion is greater than 125 mg/dL, although clinical signs of HYPOGLYCEMIA
hyperglycemia do not develop until the renal tubular thresh-
old for the resorption of glucose is exceeded. In dogs this Etiology
typically occurs whenever the blood glucose concentration Hypoglycemia is present if the blood glucose concentration
exceeds 180 to 220 mg/dL. The threshold for glucose resorp- is less than 60 mg/dL. It typically results from excessive
tion appears to be more variable in cats, ranging from 200 uptake of glucose by normal cells (e.g., during periods of
to 280 mg/dL. Glycosuria causes an osmotic diuresis, which hyperinsulinism as with a β-cell tumor or xylitol ingestion)
in turn causes polyuria and polydipsia, the hallmark clinical or neoplastic cells, impaired hepatic gluconeogenesis and
signs of severe hyperglycemia. The most common cause of glycogenolysis (e.g., portal shunt, hepatic cirrhosis), a defi-
hyperglycemia and glycosuria is diabetes mellitus. Severe ciency in diabetogenic hormones (e.g., hypocortisolism), an
hyperglycemia without glycosuria also occurs commonly in inadequate dietary intake of glucose and other substrates
cats with stress-induced hyperglycemia, presumably result- required for hepatic gluconeogenesis (e.g., anorexia in the
ing from the secretion of catecholamines. Transient gly- neonate or in toy breeds), or a combination of these mecha-
cosuria (typically < 1% on urine glucose test strips) may nisms (e.g., sepsis; Box 49.2). Iatrogenic hypoglycemia is a
occur in some cats with severe or prolonged stress-induced common problem resulting from overzealous insulin admin-
hyperglycemia. istration in diabetic dogs and cats.
Prolonged storage of blood before separation of serum
Clinical Features or plasma causes the glucose concentration to decrease at
Hyperglycemia of between 125 and 180 mg/dL (often as a rate of approximately 7 mg/dL/h. Glycolysis by red and
high as 250 mg/dL in cats) is clinically silent and is an white blood cells becomes even more apparent in dogs and
unsuspected finding encountered during blood testing for cats with erythrocytosis, leukocytosis, or sepsis. Therefore
another reason. If a dog or cat with mild hyperglycemia whole blood obtained for the measurement of glucose con-
(<180 mg/dL) and no glycosuria is seen because of poly- centration should be separated soon after collection (within
uria and polydipsia, a disorder other than overt diabetes 30 minutes), and the serum or plasma should be refrig-
mellitus should be suspected. Mild hyperglycemia can erated or frozen until the assay is performed to minimize
occur in some dogs and cats up to 2 hours after consump- artifactual lowering of the blood glucose concentration.
tion of diets containing increased quantities of mono- Glucose determinations from separated and refrigerated
saccharides and disaccharides, corn syrup, or propylene plasma or serum are reliable for as long as 48 hours after
glycol; during intravenous (IV) administration of total separation and refrigeration of the specimen. Alternatively,
parenteral nutrition fluids; in stressed, agitated, or excit- plasma can be collected in sodium fluoride tubes. Unfortu-
able cats and dogs; in animals in the early stages of dia- nately, hemolysis is common in blood collected in sodium
betes mellitus (i.e., subclinical diabetes); and in animals fluoride–treated tubes, which can result in slight decrements
with disorders and drugs causing insulin resistance (Box in glucose values related to methodologic problems in labo-
49.1). A diagnostic evaluation for disorders causing insulin ratory determinations. Blood glucose values as determined
resistance is indicated if mild hyperglycemia is found to by many portable home blood glucose–monitoring devices
persist in a fasted, unstressed dog or cat, especially if the designed for use by human patients with diabetes are almost

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